Migrate from Next.js to SvelteKit

- Replace Next.js app with SvelteKit + adapter-node
- basePath /bodenfeuchte configured in svelte.config.js
- MQTT listener starts via hooks.server.ts on server boot
- Chart.js replaces Recharts for the moisture graph
- Dockerfile simplified: single build step, node build output
- Removed custom server.ts (no longer needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,23 +1,8 @@
-# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
-
 # dependencies
 /node_modules
-/.pnp
-.pnp.*
-.yarn/*
-!.yarn/patches
-!.yarn/plugins
-!.yarn/releases
-!.yarn/versions
 
-# testing
-/coverage
-
-# next.js
-/.next/
-/out/
-
-# production
+# SvelteKit build output
+/.svelte-kit
 /build
 
 # misc
@@ -30,7 +15,7 @@ yarn-debug.log*
 yarn-error.log*
 .pnpm-debug.log*
 
-# env files (can opt-in for committing if needed)
+# env files
 .env
 .env.local
 .env.*.local
@@ -38,12 +23,5 @@ yarn-error.log*
 # sqlite data
 /data/*.db
 
-# compiled server
-/dist
-
-# vercel
-.vercel
-
 # typescript
 *.tsbuildinfo
-next-env.d.ts